Automatic resetting overload switch



2, 1952 A. GOLDSMITH AUTOMATIC 'RESETTING OVERLOAD SWITCH Sept.

FiledMay 51, 1951 2 SEETSr-SHEEII FIG. 3.

FIG. I.

FIG. 4.

FIG. 5.

INVENTOR AARON GOLDSMlTH ATTORNEY Sept. 2, 1952 A. GOLDSMITH, 6 555-AUTOMATIC RESETTING ovzmomswryca Filed May 51, 1951 zggmg-sasg z FIG. 8.

INVENTOR AARON GOLDSMITH ATTORNEY Patented Sept. 2, 1952 UNITED STATESPATENT OFFICE .sAUT-OMATIC RESETTING OVERLGAD SWITCH Aaron Goldsmith,Los Angeles, Calif. Application May 31, 1951, Serial No. 229,120

12 Claims. 1

This invention'relates to an automatic resettin overload saietyswitch.

My invention relates particularly to overload safety switches of thetype having a circuit breaking element capable of being used for manytimes and .designedto replace .the ordinary screw plug fuse in which thebreaking of the circuit is effectedbythe melting of a fusiblematerial.

The. .principal object of the invention is to providean overload .safetyswitch of simple and in expensive construction which will break anelectrical "circuit at a pre-determined. overload current. Anotherobject is to provide an overload safety switch which may be constructedof small enough dimensions to be contained in a screw plug type housing,and adapted for use in the. same kind of screw plug base. Another objectof the invention is to provide an overload safety switchwhich-automatically resets the circuit after the cause of the overloadhas been removed. .Another object is to provide an overload safetyswitch which will automatically reset itself when the entire load isdisconnected from the circuit. A further object is to provide anoverload safety switch completely enclosed in a sealed gas filled bulband which is free from external sparking. A still further object is toprovide an overload safety switch which visually indicates whether ornotthe circuit is overloaded and open, .or closed'and not. in overloadedcondition. These and other objects are'attained by my invention whichwill be understood from the following description, reference being madeto the accompanying drawings in which;

Figure 1. is a side elevational view of my invention .inthe .form of aconventional screw base p us;

Figure 2: is a front endv view of the same;

Figure 3 is a rear end viewof the same;

Figure. 4 is; alongitudinal sectional view taken on the line 44 ofFigure 2;

Figure 5 is a sectional. view taken. on the line 5-5 of Figure 4.;

Figure 6: is a sectional. view taken on the line G -6 of Figure 4;.

Figure '7 is a sectional. view taken on the line 'l-"l of'Figure 4showing an alternative arrangement of the electrical .connection betweenthe plug end terminal and the switch;

Figure 8 is a longitudinal section showing an otheraltemative form of myinvention;

Figure 9 is 'a cross-sectional view taken on the line 9--9 of-Figure 8and Figure 10 isra crossesectional viewtaken on the cm- Ill-! 0 ofFigure 8.

Referring to the drawings which show a preferred form of my invention,my resetting overload switch consists of a housing I I which isgenerally cylindrical in shape and made of insulating material suchasporcelain, being provided witha screw threaded portion I2, and having,a front opening I3 leading to a cylindrical cavity 15, which is adaptedto receive a rotatable switch mounting member I4. The screw threadedportion I2 of the housing I I is covered with a-co-pper or brasscontacting sheath I6 which is adapted to make electrical contact with ascrew threaded socket in which the housing II is adapted to be inserted.The sheath I6 is electrically connected by the wire I! to a metallicband I8 on the inside of the cylindrical cavity I5 adjacent the. "frontopening I3. An end contact terminal I9 is pro;- vided on the closed endof the housing I-l, electrically insulated from the sheath I6, the endterminal being electrically connected by the wire 20 to a contactingband 22, which is disposed in the cylindrical wall of the cavity I5adjacent the inside end of said cavity.

As shown in Figure 7, a fusible link 2|. may alternatively be providedbetween the wire 20 and the band 22 as. a safety device to protect thecircuit in the event that the switch parts fail to operate, or becomefixed and provide continuous flow of current and continuous. overload.cone ditions. z

The switch mounting member I4 consists of .a cylindrical insulating bodyhaving a cavity in which the switch member 23 is mounted,. the mountingmember I4 being also provided with a knurled ring on the forward end bywhich the switch member may be rotated, and anindexing mark 25 showingthe axial position of the member.

The switch itself consists of a bulb 26 preferablymade of glass ortransparent plastic, which is generally cylindricalin shape, both endsbeing closed, and having. a spring. bar orwir e slide contact member 2!sealed into the side wall of the bulb at a position which allows theexterior end of said spring contact member?! to make sliding contactwith the band 22 in the inside wall of the cavity I5 of the housing. Thespring wire member 21 at its end inside the bulb 26 is connected to thecross pin 23 which is embedded in the opposite walls of the bulb 26. Abi-metal lic bar 29 composed of superimposed stripsof metal havingdifferent coefiicients of expansion, and formed into a spiral coil 30 atone end is at tached to the cross pin 28, the arm portion 31 ex tendingforwardly within the bulb 26... and having I 3 a downwardly bentcontacting arm 32 at its end opposite said spring coil. The bi-metallicelement is so arranged that when the circuit is operating normallywithout overload, the contacting arm 32 dips into a pool of mercury 33formed in a depression 34 in the bulb 25 near the forward end of saidbulb. The pool of mercury 33 is connected through the shell of the bulb26 by a second spring bar or wire member 35, which is adapted to makecontact with the connecting band i8 disposed in the cylindrical cavity lof the housing adjacent the front opening !3. When current passingthrough the bi-metallic bar 29 is great enough to cause heating of thebi-metallic bar 29, the contacting arm 32 of said bar rises out of thepool of mercury 33 and takes the position shown in broken lines inFigure 4. When the current flowing through the metallic bar 29 exceedsthe pre-determined safe amount, then the bi-metallic element expands soas to cause the contacting arm 32 to rise out of the mercury 33 andbreak the contact. The end of the contacting arm 32 is provided with ahigh resistance contact point 36 and as it goes out of the mercury, itbecomes hot enough to vaporize the mercury and to cause the mercuryvapor and filler gas to ionize and glow, under which condition the gascontent of the bulb 26 will carry enough current to heat the inside ofthe bulb and cause the bi-metallic bar 29 to remain in position out ofthe mercury until all the load is removed from the circuit. When theload is removed from the circuit flowing through the device, thetemperature inside the bulb ill drop and this in turn will cause thebi-metallic bar 29 to drop backvinto the mercury 33 and the circuit willbe a ain closed.

The bulb 26 may be filled with various gases such as nitrogen, neon,helium, etc., or mixtures of gases at various pressures, to give dfferent colors during the glowing period and these differences in colormay be used as a visual indicator of the current carrying capacity ofthe switch. The bi-metallic element 29 may be made of suitablecross-sectional area so that it will operate at selected currentcapacities.

The switch mounting member [4 is arranged to be rotated in thecylindrical cavity !5 so that the pool of mercury 33 may be positionedfor operation at the lowest point in the bulb 26, and the circuit may bemanually disconnected merely by rotating the switch member mounting l4so that the mercury is not in the depression 34. It if is desired toreset the switch without disconnecting all of the current load, then theswitch mounting member may be momentarily removed from the cavity andagain replaced in the usual manner.

A permanent magnet 38 may alternatively be imbedded in the wall of theswitch mounting member [4 to hold the bi-metallic bar 29 in thedisconnected position, and under certain operating conditions preventoscillation of this arm. The presence of the magnet prevents the armfrom dropping back into the mercury until the temperature has eitherdecreased to the point where the energy of the spring coil 30 breaks themagnetic holding force and positively forces the contacting arm 32 intothe pool, or under some conditions until light tapping of the outside ofthe device breaks the magnetic hold after the temperature has decreased.If the bi-metallic member is not attracted by a magnet, a small ironarmature may be suitably attached to the arm 3|.

The second alternative structure shown in Figures 8 and 9 provides meansfor immediate disconnection of the circuit in the event that a suddenheavy current flows through the device, as in the event of a shortcircuit. An electromagnet is provided which attracts the arm 3|, andcauses it to rise quickly to break the circuit. The iron strip 38A isplaced in position adjacent the arm 3 I, preferably inside the bulb 2B,and the copper coil 39 is embedded in the switch mounting member I4,being electrically connected in series between spring contact member 21Aand the connecting bar 21B to the bi-metallic bar 29 through the coiledspring portion 30. The magnetic fiux produced by a heavy current willcause the arm 3| to rise and break the circuit, and will drop back againto re-connect the circuit when the normal load on the circuit isreestablished. This device avoids the use of the fusible link 2|, andthe renewing thereof, since this circuit breaker is fully automatic.

The advantages of my automatic resetting overload switch will beapparent. The device does not require any manual resetting if thecurrent load is removed from the circuit in which case the circuit isagain closed when the gas in the bulb ceases to conduct current andcools oil. The condition of the contacting arm 32 may be observedthrough the window 31 in the knurled ring 24 and also the glowing of thegas in the pool may be observed through this window when the switch isout of contact. In the second alternative form, the device is fullyautomaticv in re-establishing connection in the circuit after anymagnitude of overload current.

I claim:

1. An automatic resetting overload switch comprising a housing havingtwo external terminals adapted to make electrical connection in anelectric power circuit, said housing having an axial cylindrical cavity;a bulb mounting member arranged in said cavity and adapted to be turnedaxially therein; a gas-filled breaker switch bulb mounted in saidmounting member, said bulb having a mercury well adjacent the front endthereof, and having a sealedin contact wire in the bottom of saidmercury Well, and also having a lead-in wire adjacent the rear end ofsaid bulb; a globule of mercury in said well; means to connect saidsealed-in contact wire with one of said external contact members; meansto connect said lead-in wire to the other of said external contactmembers; and a bi-metallic bar mounted within said bulb and arranged forlever movement at one end, said bar having a dipping point at the lowerend arranged to make contact with the mercury in said well, said dippingpoint being arranged to break contact with said mercury in said wellwhen said bar is over-heated by the passage of an overload currentthrough said switch bulb.

2. A screw plug type housing having an externally threaded contactingsurface and an external central end contact button adapted to makeelectrical connection in an electric power circuit, said housing havingan axial cylindrical cavity; a bulb mounting member mounted in andadapted to be turned axially in said cavity; .-a gas-filled breakerswitch bulb mounted in said mounting member, said bulb having a mercurywell adjacent the front end thereof, and having a sealed-in contact wirein the bottom of said mercury well, and having a lead-in wire adjacentthe rear end of said bulb; a globule of mercury in said well; means toconnect said -'5 sealed-in contact wi-re with one of esaid externalcontact members; -means; to connectsaiddead -in wire tofthe other ofsaid externalcontactmembers;- anda bi-inetallic ba-rmounted withinsaidbulb and arranged 'forlever movement at vone end; said'bar having"adipping point at the lever end arrangedto make contact-with the:mercury insaid -well,- said dipping point being arranged to breakcontact with said mercury in said well when said bar isover-h'eatedby-the passage of an overload current through said switch bulb.

3. A screw plug type housing having an externally threaded contactingsurface and an external central end contact button adapted to makeseries electrical connection in an electric power circuit, said housinghaving an axial cylindrical cavity; a bulb mounting member mounted inand adapted to be turned axially in said cavity; a gas-filled breakerswitch bulb mounted in said mounting member, said bulb having a mercurywell adjacent the front end thereof, and having a sealed-in contact wirein the bottom of said mercury well, and also having a lead-in wireadjacent the rear end of said bulb; a globule of mercury in said well;means to connect said sealed-in contact wire with one of said externalcontact members; means to connect said lead-in wire to the other of saidexternal contact members; and a bi-metallic bar shaped as a spiralspring coil at one end and bent down to a dipping point at the other,said bar being mounted within said bulb for lever movement on saidspring coil, said dipping point being arranged to break contact withsaid mercury in said well when said bar is over-heated by the passage ofan overload current through said switch bulb.

4. A screw plug type housing having an externally threaded contactingsurface and an external central end contact button adapted to makeseries electrical connection in an electric power circuit, said housinghaving an axial cylindrical cavity; a bulb mounting member mounted inand adapted to be turned axially in said cavity; a gas-filled breakerswitch bulb mounted in said mounting member, said bulb having a mercurywell adjacent the front end thereof, and having a sealed-in contact wirein the bottom of said mercury well, and also having a lead-in wireadjacent the rear end of said bulb; a-globule of mercury in said well;means to connect said sealed-in contact wire with one of said externalcontact members; means to connect said lead-in wire to the other of saidexternal contact members; and a bi-metallic bar shaped as a spiralspring coil at one end and bent down to a dipping point at the other,said bar being mounted within said bulb for lever movement on saidspring coil, said dipping point being arranged to break contact withsaid mercury in said well when said bar is over-heated by the passage ofan overload current through said switch bulb.

5, The device claimed in claim 1, in which a permanent magnet isattached to said switch bulb at a position to attract said bi-metallicbar when said bar is out of contact with said mercury pool, whereby saidcontact remains broken until a mechanical force overcoming theattractive force of said magnet acts upon said bar to release it fromsaid magnet.

6. The device claimed in claim 1, in which said dipping point has highelectrical resistance relative to said bi-metallic bar, whereby heat isgenerated and mercury vaporized when said point breaks contact with saidpool of mercury during '6 overloading of current through .s'a-ldbimetallic bar: V

7; A screw :plug type housir'ig havin'g zanex ternall-y threadedcontacti-ng surface andan external; central -end contactbutton adaptedtomake series electrical-connection in an electric power-circuit, saidhousing hav ing an axial cylindrical cavity; twoconcentricelectricalcontact rings embeddedin the'j'surface ofsaid -caiiity, saidrings being electrically connected irespectively to said externalthreaded contact surface and to said contact button; a bulb mountingmember mounted in and adapted to be turned axially in said cavity; agas-filled breaker switch bulb mounted in said mounting member, saidbulb having a mercury well adjacent the front end thereof and having asealed-in contact wire in the bottom of said mercury well, and alsohaving a lead-in wire adjacent the rear end of said bulb; a globule ofmercury in said well; spring means connecting said sealed-in contactwire with one of said contact rings; spring means connecting saidlead-in wire to the other of said contact rings; and a bi-metallic barshaped as a spiral spring coil at one end and bent down to a dippingpoint at the other, said bar being mounted within said bulb for levermovement on said spring coil, said dipping point being arranged to breakcontact with said mercury in said well when said bar is over-heated bythe passage of an overload current through said switch bulb.

8. The device claimed in claim '7, in which said dipping point has highelectrical resistance relative to said bi-metallic bar, whereby heat isgenerated and mercury vaporized when said point breaks contact with saidpool of mercury during overloading of current through said bi-metallicbar.

9. The device claimed in claim 2, in which a fusible link is disposed inthe lead-in wire circuit between said contact button and saidbi-metallic bar.

10. The device claimed in claim 1, in which an electromagnet is disposedin said switch in position to attract said bi-metallic bar when said baris in contact with said mercury pool, the coil of said electromagnetbeing connected in the circuit of said switch, whereby when a heavyoverload current passes through said circuit, said bi-metallic barbreaks contact with said mercury pool irrespective of its bending due toheating.

1. The device claimed in claim 2, in which an electromagnet is disposedin said switch in position to attract said bi-metallic bar when said baris in contact with said mercury pool, the coil of said electro-magnetbeing connected in the circuit of said switch, whereby when a heavyoverload current passes through said circuit, said bimetallic bar breakscontact with said mercury pool irrespective of its bending due toheating.

12. A screw plug type housing having an externally threaded contactingsurface and an external central end contact button adapted to makeelectrical connection in an electric power circuit, said housing havingan axial cylindrical cavity; a bulb mounting member mounted in andadapted to be turned axially in said cavity, said bulb mounting memberhaving embedded therein a magnetic coil adapted to activate an iron corein a switch bulb; a gas-filled breaker switch bulb mounted in saidmounting member, said bulb having a mercury well adjacent the front endthereof and having a sealed-in contact wire in the bottom of saidmercury well, and having a 7 lead-in wire adjacent the rear end of saidbulb; a globule of mercury in said well; means to connect said sealed-incontact wire with one of said external contact members; means to connectsaid lead-in wire to the other of said external contact 5 members; abi-metallic bar mounted within said bulb and for lever movement at oneend, said bar having a dipping point at the lever end arranged to makecontact with the mercury in said well,

said dipping point being arranged to break con- 10 8 tact with saidmercury in said well when said bar is over-heated by the passage of anoverload current through said switch bulb; and a magnet bar in said bulbadjacent said bi-metallic bar, the magnet coil in said mounting memberbeing electrically connected in the circuit passing through said breakerswitch.

AARON GOLDSMITH.

No references cited.

